Abstract

Between December 1811 and March 1812, the largest series of earthquakes recorded in United States struck the Upper Mississippi Embayment, centered near New Madrid, MO. The region was subjected to repeated episodes of wide-scale liquefaction, ground subsidence and uplift, as well as landslides and earth movement towards stream channels. In his 1912 report on the New Madrid earthquakes, Myron Fuller described numerous features that exhibited characteristics and morphology similar to lateral spread features associated with the 1964 Alaska earthquake. However, before this report, no lateral spread features were substantially verified and characterized within the New Madrid Seismic Zone (NMSZ). The authors have used topographic mapping protocols to identify areas of seismically induced landslippage, including lateral spread features, along Crowley's Ridge in the western NMSZ. It is thought that the lateral spread features formed in response to liquefaction of underlying confined sand layers during ground shaking associated with the New Madrid earthquakes. Lateral spreads, like other types of landslippage, exhibit fairly specific topographic signatures that can be identified on contour maps. The authors used digital map products in combination with Geographic Information Systems programs to find and delineate areas with topographic signatures representative of lateral spread features. For verification of the features, the authors are using geophysical and field methods, including ground penetrating radar (GPR) and electrical resistivity, to determine whether the suspect features are indeed lateral spreads.